Philadelphia is a red brick city. Drive through almost any neighborhood built before 1940 and the dominant material of the row home facades — the walls, the chimneys, the retaining walls, the steps — is brick: a specific, warm-toned, iron-oxide-rich clay brick fired in kilns that once dotted the Delaware Valley from Bucks County to Delaware.
This is not an accident of taste. It is a consequence of geology, economics, and industrial history that shaped the built environment of the entire region. Understanding Philadelphia brick — where it came from, what it is, how it behaves, and how to care for it — is foundational knowledge for anyone who owns or loves a row home in this city.
Where Philadelphia Brick Comes From
The Delaware Valley sits on deposits of red shale and clay that, when fired, produce a characteristically warm brick with iron oxide content that gives it a range of colors from buff-orange to deep burgundy. The Wissahickon Creek watershed and the areas around Norristown and Conshohocken were major centers of brick production in the nineteenth century. Brickyards operated along the Delaware and Schuylkill rivers, taking advantage of water transportation to deliver materials to building sites across the city.
At the peak of Philadelphia’s row home construction — roughly 1870 to 1930 — the city and its surrounding region supported hundreds of brickyards. The output was enormous: millions of bricks per year, produced to meet the demand of a city building itself street by street, block by block. The bricks varied in quality and dimension from yard to yard, which is why careful examination of a row home facade often reveals subtle variations in color and texture — each course reflecting the specific source of that batch of material.
The Anatomy of a Brick Wall
A Philadelphia row home exterior wall is not a single wythe of brick. It is a composite assembly: typically two or three wythes of brick bonded together with headers — bricks laid perpendicular to the wall face, passing from the outer to the inner wythe — and mortar. The result is a wall 8 to 12 inches thick that is structurally self-supporting, highly fire-resistant, and, if properly maintained, essentially permanent.
The mortar between the bricks is as important as the brick itself, and it is the mortar that most commonly fails. Historic Philadelphia row homes used lime-based mortar — a mix of hydrated lime, sand, and water — that is softer than the brick it holds. This is intentional: a mortar that is softer than the brick allows the mortar to absorb stress (from thermal movement, from settlement, from moisture cycling) rather than transmitting it to the brick face. When the mortar fails, it can be repointed. If a harder mortar — Portland cement-based — is used to repoint a historic lime-mortar wall, the stress goes to the brick instead, and the brick face spalls.
Reading Your Brick
The condition of a row home’s brick tells a story. Here is what to look for:
Spalling. Brick faces that have broken off or are flaking indicate water infiltration followed by freeze-thaw cycling, or a mortar repointing with Portland cement that is too hard for the historic brick. Spalling is serious and progressive — once a brick face begins to spall, it accelerates. Spalled bricks need to be replaced or, in some cases, consolidated with a penetrating consolidant applied by a masonry conservator.
Efflorescence. The white crystalline deposits that appear on brick faces are mineral salts carried to the surface by water moving through the wall. Efflorescence itself is cosmetic, but it signals that water is actively moving through the masonry — which means there is a source somewhere (failed flashing, deteriorated mortar, improper grade drainage) that needs to be addressed.
Mortar joint condition. Run your hand along the mortar joints. If mortar is loose, crumbling, or missing in sections more than a quarter-inch deep, repointing is needed. Failing mortar allows water infiltration that degrades both the wall assembly and the interior.
Color variation. Areas of darker or lighter brick compared to the overall facade often indicate past repairs — either new bricks that have not yet weathered to match, or areas where the surface has been cleaned or treated. This is informational, not necessarily problematic.
Maintenance: What Row Home Owners Should Know
Philadelphia brick requires relatively little maintenance if the basics are attended to. The critical items:
Keep mortar joints in good condition. Repoint with a lime-based mortar matched to the historic mortar in composition and joint profile. Do not use Portland cement mortars on pre-1940 brick.
Maintain flashing. The flashing at the roof-wall intersection, at window and door lintels, and at any horizontal ledge is the primary defense against water infiltration. Failed flashing is the most common source of serious masonry damage.
Do not paint unpainted brick. Paint traps moisture in the masonry and, when it eventually fails, takes brick face with it. If your brick is currently painted, consult a masonry professional before attempting removal — improper paint removal damages brick.
Be cautious with pressure washing. High-pressure washing drives water into the masonry and can damage soft historic brick. Low-pressure washing with appropriate cleaners is safe; high-pressure is not.
The brick that built Philadelphia is, at its best, a nearly maintenance-free material. The row homes that have survived in the best condition are, without exception, buildings where someone paid attention to the small things — the mortar joints, the flashing, the drainage at grade — before the small things became large ones. The material rewards attention.